KANDAHAR, Afghanistan — A suicide bomber killed two Americans and five Afghans yesterday outside a security contractor’s southern Afghan compound, officials and witnesses said.

The bomber struck as the victims exited the Kandahar offices of the Houston-based U.S. Protection and Investigations security company, a company official, Rohullah Khan, said. Three other people were wounded, he said.

The blast, the sixth suicide attack in Kandahar province in nine days, went off opposite the offices of the Canadian Provincial Reconstruction Team, a military team charged with rebuilding efforts in the area.

Provincial police chief Asmatullah Alizai said two foreigners, four Afghan policemen, and a translator were killed.

USPI employee Mohammad Aszal said the two foreign victims were American.

Qari Yousaf Ahmadi, who said he was a spokesman for the Taliban in southern Afghanistan, contacted the Associated Press and said the militant group was responsible for the attack. Mr. Ahmadi’s exact ties to the militants are not known.

Near-daily attacks plague the southern provinces of Afghanistan — the former stronghold of the hard-line Taliban regime, where the central government wields little power.

Taliban militants have carried out a record number of suicide and roadside bombings this year. A growing insurgency, especially in the country’s South and East, has left close to 4,000 people dead.

Despite the spike in suicide bombings in the past nine days, NATO said yesterday that the overall number of coordinated insurgency attacks across the country is decreasing.

The number of major attacks in November was 449, a drop of nearly 50% compared to 869 in September, the chief NATO spokesman in Afghanistan, Brigadier Richard Nugee, said.